PIV experimental analysis of the escape phenomenon of air spraying jet in factories

Inefficient air spraying can release a large amount of paint particles from a spraying jet, which can seriously endanger the health of operators. The flow field characteristics of air atomizing spray guns have a significant influence on spraying efficiency. To investigate the reasons for the escape of paint particles during air spraying, improve efficiency at the source and curb the escape of pollutants into a factory building, this study measured the whole flow field of an air spray gun via a 2D particle image velocimetry (PIV) system. The results showed that the spraying jet velocity reached a maximum of 28 m/s near the spray nozzle with a Reynolds number of 3000 and subsequently decayed rapidly due to the strong momentum exchange with the surrounding air. The radial velocity at the junction of paint mist and air first increases and then decreases (maximum 0.5 m/s). The turbulence intensity was relatively high at the spraying jet boundary. In addition, the spay flow at the nozzle and the jet boundary showed high intermittency. The turbulence structures were studied by proper orthogonal decomposition (POD). The results indicated that the radial velocity of spray was the major source underlying the development of spraying jet radial diffusion. Finally, the spraying efficiency was calculated to be between 53 % and 58 %. For air spraying, suppressing radial movement can improve spraying efficiency by up to 40 %, which is essential to controlling the escape of paint mist and improving the working environment in spray booths.